The use of adhesives, including asphaltic compounds, to provide a bond between roofing shingles when applied to a roof is known. During a typical shingle manufacturing process, a pattern of adhesive is applied to the headlap portion of the shingles so that the tab portion of the subsequently laid course of shingles on the roof will adhere to the headlap portion of the lower course, to help prevent wind uplift of the shingles. To seal properly, most adhesives or sealants require relatively high roof temperatures. U.S. Pat. No. 4,559,267 discloses an adhesive, of a compounded bitumen containing 3-20% rubber and/or thermoplastic resins, which requires an activation temperature of at least 90.degree. F. Many other adhesives require roof temperatures of about 135.degree. F. or higher. In relatively colder climates, these roof temperatures may never be reached or in certain climates, these temperatures may not be reached until seasons subsequent to installation, which may be months later. Consequently, under conditions where relatively low temperatures do not permit proper sealing of the adhesive, the shingles may be susceptible to blow-off in relatively higher winds. Another problem with conventional sealants is that colder temperatures tend to cause the sealant on properly sealed shingles to become brittle and crack, resulting in bond failures and blow-offs.
U.S. Pat. No. 3,138,897 to McCorkle addresses the blow-off problem by using an adhesive strip on the shingle composed of distinct bands of two different adhesives one is pressure sensitive while the other is temperature sensitive. As with conventional adhesives, the temperature sensitive adhesive of McCorkle seals at relatively higher temperatures and since it doesn't even begin to get tacky until about 70.degree. F., a second adhesive must be used to permit sticking at lower temperatures, which is the pressure sensitive adhesive. The pressure sensitive adhesive is effective only at lower temperatures since it loses its tackiness beyond temperatures of about 100.degree. F.
An asphalt-based adhesive has now been discovered which is both pressure and temperature sensitive and effectively works to greatly reduce the vulnerability of a shingle to the cold and wind. The adhesive of the instant invention remains tacky at roof temperatures as low as 50.degree. F. to provide a good initial bond upon shingle installation at these temperatures. While the adhesive seals the shingles at temperatures required by most sealants, i.e., 135.degree. F. or higher, this adhesive also effectively seals the shingles at roof temperatures as low as 50.degree. F. This means that air temperature may be as low as 25.degree. F. Additionally, the adhesive retains appreciable strength and flexibility at lower temperatures which means that the adhesive does not get brittle and crack and will not break an already formed seal.
A further advantage of having to apply only a single adhesive to the shingle is provided by the adhesive of the instant invention. The cost benefits of applying one sealant as opposed to two or more different sealants will become readily apparent to those skilled in the art, particularly when viewed from the standpoint of shingle manufacturing.